Recently, along with the increased popularity of picture-taking instruments such as cameras, there increase picture-taking chances by use of a silver halide light sensitive photographic material (hereinafter, also referred to as a photographic material). As a result, further enhancement in sensitivity and image quality has been desired by the public.
One dominant factor for enhancing sensitivity and image quality of the photographic material concerns silver halide grains, and there has been on going development of silver halide grains aimed at enhancement of sensitivity and image quality. As is well recognized in the art, however, in conjunction with decreasing the silver halide grain size for enhancing image quality, the sensitivity tends to be lowered, and enhancing both sensitivity and image quality has its limits.
To further enhance the sensitivity and the image quality have been studied techniques for enhancing the ratio of sensitivity to grain size of the grain. One technique is to employ tabular silver halide grains, as described in JP-A 58-111935, 58-111936, 58-111937, 58-113927 and 59-99433 (herein, the term, JP-A means a unexamined, published Japanese Patent Application). When compared to a silver halide regular crystal grain such as octahedral, tetradecahedral or hexahedral grain, the surface area of a tabular silver halide grain is larger than that of the regular grain having the same volume, allowing more sensitizing dyes to be adsorbed onto the silver halide grain surface and advantageously leading to further enhancement of sensitivity. JP-A 6-230491, 6-235988, 6-258745 and 6-289516 disclose the use of tabular silver halide grains having still higher aspect ratios (i.e., a ratio of grain diameter to thickness).
JP-A 63-92942 discloses a technique of providing a core having a high silver iodide content in the interior of tabular silver halide grains and JP-A 63-163541 discloses a technique of employing tabular silver grains having a ratio of grain thickness to a longest spacing between twin planes of 5 or more, each leading to improvements in sensitivity and image quality.
JP-A 63-106746 discloses tabular silver halide grains having a substantially layered structure in the direction parallel to the two opposing major faces. JP-A 1-279237 discloses tabular silver halide grains having a layer structure bounded by a plane substantially parallel to the two opposing major faces and further having an outermost layer having an average silver iodide content higher by 1 mol % or more than the average overall silver iodide content.
JP-A 3-12445 discloses silver halide grains having parallel twin planes and interfacial layers containing regions which are different in the silver iodide content; JP-A 63-305343 discloses tabular silver halide grains having development initiating points in the vicinity of the grain corner; and JP-A 2-34 discloses silver halide grains having (100) and (111) faces.
JP-A 1-183644 discloses a technique of employing tabular silver halide grains characterized in that the silver iodide content distribution of iodide containing silver halide grains is completely uniform.
There is also disclosed a technique of controlling carriers through metal doping, i.e., a technique of improving photographic performance by allowing a polyvalent metal oxide to be contained within the grain.
JP-A 3-196135 and 3-189641 disclose a silver halide emulsion which was prepared in the presence of an oxidizing agent with respect to silver and effects on sensitivity and fog of a photographic material by use of the emulsion. Further, JP-A 63-220238 discloses a technique of a silver halide emulsion containing tabular grains in which the position of dislocation lines is limited; JP-3-175440 discloses a technique of employing a silver halide emulsion containing tabular grains in which dislocation lines are concentrated in the vicinity of the grain corners; JP-B 3-18695 (herein, the term, JP-B means published Japanese Patent) discloses a technique of silver halide grains having a distinctive core/shell structure; and JP-B 3-31245 discloses silver halide grains having a core/shell type three-layered structure.
JP-A 6-11781, 6-11782, 6-27564, 6-250309, 6-250310, 6-250311, 6-250313 and 6-242527 each disclose techniques for achieving enhanced sensitivity and improved fog and pressure resistance by the use of an iodide ion-releasing compound during grain formation.
However, the prior art described above is limited in achieving enhancement of both sensitivity and image quality and insufficient for satisfying requirements in recent photographic materials, therefore, development of a technique superior to the prior art is desired.
To subject silver halide grains more effectively to chemical sensitization and spectral sensitization, development of a technique to enable more accurate control of sensitivity specks and halide composition on the silver halide grain surface is needed, and studies which have been made so far in the art were insufficient to meet this need.